The present invention relates to the polymerization of furan resins, and more particularly to the hardening or curing of furan resins in the presence of a particular catalyst.
Furan resins obtained by condensing one or more furan alcohols have been known for at least about forty years. The condensation of furan alcohol achieved in the presence of an acid catalyst yields a poly (furfuryl alcohol) which is a viscous liquid. This liquid is hardened by using an acidic catalyst such as an inorganic acid, for instance, phosphoric acid, sulfuric acid or hydrochloric acid or an organic acid, for example, benzenesulfonic acid, phenolsulfonic acid, paratoluenesulfonic acid or a mixture of these organic acids with inorganic acids.
Furan resins are used for the manufacture of many composite articles reinforced with suitable agents such as sand and glass fibers. Glass fibers are particularly suitable for the manufacture of furan laminate articles, but the hardening of furan resins by using known acidic catalyst yields articles which are very porous. Furan resins are also used to manufacture laminated articles comprising a layer of phenolic resin, reinforced with glass fiber mats and coated on one side or on two sides with a furan resin layer bonded optionally to a thermosetting resin, for example, a polyester resin. In this case, the laminates obtained by the hardening of furan resins with aqueous acidic solutions exhibit poor fire resistance on the furan layer side.